Respiratory tolerance is inhibited by the administration of corticosteroids

Corticosteroids constitute the most effective current anti-inflammatory therapy for acute and chronic forms of allergic diseases and asthma. Corticosteroids are highly effective in inhibiting the effector function of Th2 cells, eosinophils, and epithelial cells. However, treatment with corticosteroids may also limit beneficial T cell responses, including respiratory tolerance and the development of regulatory T cells (T(Reg)), which actively suppress inflammation in allergic diseases. To examine this possibility, we investigated the effects of corticosteroid administration on the development of respiratory tolerance. Respiratory exposure to Ag-induced T cell tolerance and prevented the subsequent development of allergen-induced airway hyperreactivity. However, treatment with dexamethasone during the delivery of respiratory Ag prevented tolerance, such that allergen sensitization and severe airway hyperreactivity subsequently occurred. Treatment with dexamethasone during respiratory exposure to allergen eliminated the development of IL-10-secreting dendritic cells, which was required for the induction of IL-10-producing allergen-specific T(Reg) cells. Therefore, because allergen-specific T(Reg) cells normally develop to prevent allergic disease and asthma, our results suggest that treatment with corticosteroids, which limit the development of T(Reg) cells and tolerance to allergens, could enhance subsequent Th2 responses and aggravate the long-term course of allergic diseases and asthma.     

Cutting edge: the absence of C3 demonstrates a role for complement in Th2 effector functions in a murine model of pulmonary allergy

Asthma is a chronic disease of the lung resulting from airway obstruction. Although the initiating causes are not entirely clear, the airway inflammation in asthma is associated with Th2 lymphocytes and their cytokines, particularly IL-4, which play a prominent role in this disease by regulating airway hyperresponsiveness, eosinophil activation, and IgE synthesis. Historically, complement was not thought to contribute to the pathogenesis of asthma. However, using C3-deficient mice in an allergen-induced model of pulmonary allergy, we demonstrate that complement may impact key features of this disease. When challenged with allergen, mice deficient in C3 exhibit diminished airway hyperresponsiveness and lung eosinophilia. Furthermore, these mice also have dramatically reduced numbers of IL-4-producing cells and attenuated Ag-specific IgE and IgG1 responses. Collectively, these results demonstrate that C3-deficient mice have significantly altered allergic lung responses and indicate a role for the complement system in promoting Th2 effector functions in asthma.     

Vaccination with heat-killed Listeria as adjuvant reverses established allergen-induced airway hyperreactivity and inflammation: role of CD8+ T cells and IL-18

Asthma is a respiratory disorder characterized by airway hyperreactivity (AHR) and inflammation and is associated with high serum IgE and overproduction of IL-4, IL-5, and IL-13 by allergen-specific Th2 cells. Our previous studies demonstrated that heat-killed Listeria monocytogenes (HKL) as an adjuvant in immunotherapy successfully reversed ongoing Ag-specific Th2-dominated responses toward Th1-dominated responses, but it was unclear if such immune modulation could reverse ongoing, established disease in target organs such as the lung. In this paper we show that a single dose of Ag plus HKL as adjuvant significantly reduced AHR in a murine model for asthma and reversed established AHR when given late after allergen sensitization. HKL as adjuvant also dramatically inhibited airway inflammation, eosinophilia, and mucus production, significantly reduced Ag-specific IgE and IL-4 production, and dramatically increased Ag-specific IFN-gamma synthesis. The inhibitory effect of HKL on AHR depended on the presence of IL-12 and CD8+ T cells and was associated with an increase of IL-18 mRNA expression. Thus, our results demonstrate that HKL as an adjuvant for immunotherapy mediates immune deviation from a pathological Th2-dominated response toward a protective immune response in peripheral lymphoid tissues and in the lungs and may be clinically effective in the treatment of patients with established asthma and allergic disease.     

Requirement for CD28 in the effector phase of allergic airway inflammation

Central to the pathogenesis of allergic airway inflammation are the activation and differentiation of T lymphocytes. This process requires the participation of the CD28 costimulatory receptor. Blockade of CD28 has been demonstrated to prevent inflammation and airway hyperreactivity in a murine model of asthma. Whether this is due specifically to defects in initial T cell activation or whether effector responses are also impaired has not been determined. Using adoptive transfer studies of Ag-specific lymphocytes, we demonstrate that CD28 has a critical role in both the induction and effector phase of allergic airway inflammation. Transfer of in vitro activated and Th2-differentiated Ag-specific lymphocytes from wild-type hosts restored inflammation, but not tissue eosinophilia in CD28-deficient recipients. Furthermore, similarly activated and differentiated CD28-deficient lymphocytes were ineffective at mediating inflammation in wild-type recipients. Secondary cytokine and proliferative responses of activated Th2 cells were highly dependent on CD28 in vitro. Moreover, eosinophil recruitment to both the lung and peritoneum is impaired by the lack of CD28, suggesting a generalized defect in the ability of eosinophils to accumulate at sites of inflammation in vivo. These data identify a novel role for CD28 in the effector phase of allergic airway inflammation and suggest that inhibition of this pathway may be a useful therapeutic intervention in previously sensitized individuals.     

Schistosoma japonicum peptide SJMHE1 suppresses airway inflammation of allergic asthma in mice

Helminths and their products can shape immune responses by modulating immune cells, which are dysfunctional in inflammatory diseases such as asthma. We previously identified SJMHE1, a small molecule peptide from the HSP60 protein of Schistosoma japonicum. SJMHE1 can inhibit delayed‐type hypersensitivity and collagen‐induced arthritis in mice. In the present study, we evaluated this peptide's potential intervention effect and mechanism on ovalbumin‐induced asthma in mice. SJMHE1 treatment suppressed airway inflammation in allergic mice, decreased the infiltrating inflammatory cells in the lungs and bronchoalveolar lavage fluid, modulated the production of pro‐inflammatory and anti‐inflammatory cytokines in the splenocytes and lungs of allergic mice, reduced the percentage of Th2 cells and increased the proportion of Th1 and regulatory T cells (Tregs). At the same time, Foxp3 and T‐bet expression increased, and GATA3 and RORγt decreased in the lungs of allergic mice. We proved that SJMHE1 can interrupt the development of asthma by diminishing airway inflammation in mice. The down‐regulation of Th2 response and the up‐regulation of Th1 and Tregs response may contribute to the protection induced by SJMHE1 in allergic mice. SJMHE1 can serve as a novel therapy for asthma and other allergic or inflammatory diseases.     

CpG oligodeoxynucleotides can reverse Th2-associated allergic airway responses and alter the B7.1/B7.2 expression in a murine model of asthma

CpG oligodeoxynucleotides (CpG-ODN) administered during Ag sensitization or before Ag challenge can inhibit allergic pulmonary inflammation and airway hyperreactivity in murine models of asthma. In this study, we investigated whether CpG-ODN can reverse an ongoing allergic pulmonary reaction in a mouse model of asthma. AKR mice were sensitized with conalbumin followed by two intratracheal challenges at weekly intervals. CpG-ODN was administered 24 h after the first Ag challenge. CpG-ODN administration reduced Ag-specific IgE levels, bronchoalveolar lavage fluid eosinophils, mucus production, and airway hyperreactivity. We found that postchallenge CpG-ODN treatment significantly increased IFN-gamma concentrations and decreased IL-13, IL-4, and IL-5 concentrations in bronchoalveolar lavage fluids and spleen cell culture supernatants. Postchallenge CpG-ODN treatment also increased B7.1 mRNA expression and decreased B7.2 mRNA expression in lung tissues. These results suggest that CpG-ODN may have potential for treatment of allergic asthma by suppressing Th2 responses during IgE-dependent allergic airway reactions. The down-regulation of Th2 responses by CPG-ODN may be associated with regulation of the costimulatory factors B7.1 and B7.2.     

The role of interferon-gamma on immune and allergic responses

Allergic diseases have been closely related to Th2 immune responses, which are characterized by high levels of interleukin (IL) IL-4, IL-5, IL-9 and IL-13. These cytokines orchestrate the recruitment and activation of different effector cells, such as eosinophils and mast cells. These cells along with Th2 cytokines are key players on the development of chronic allergic inflammatory disorders, usually characterized by airway hyperresponsiveness, reversible airway obstruction, and airway inflammation. Accumulating evidences have shown that altering cytokine-producing profile of Th2 cells by inducing Th1 responses may be protective against Th2-related diseases such as asthma and allergy. Interferon-gamma (IFN-gamma), the principal Th1 effector cytokine, has shown to be crucial for the resolution of allergic-related immunopathologies. In fact, reduced production of this cytokine has been correlated with severe asthma. In this review, we will discuss the role of IFN-gamma during the generation of immune responses and its influence on allergic inflammation models, emphasizing its biologic properties during the different aspects of allergic responses.     

Maternal transmission of resistance to development of allergic airway disease

Parental phenotype is known to influence the inheritance of atopic diseases, such as allergic asthma, with a maternal history being a more significant risk factor for progeny than paternal history. We hypothesized that recall Th1- or Th2-type immune responses during pregnancy would result in transfer of maternal factors that would differentially impact development of immune responsiveness in offspring. Following weaning, susceptibility and severity of allergic airway disease (a murine model of human asthma) was evaluated in progeny, disease being elicited by immunization with OVA-Al(OH)(3) and challenge with aerosolized OVA. We found that progeny of mothers with Th1-biased immunity to OVA subjected to recall aerosol challenge during pregnancy had reduced levels of Ag-specific IgE and airway eosinophilia compared with progeny of mothers with Th2-biased immunity to OVA or naive mothers. Interestingly, progeny of mothers with Th1-type immunity to a heterologous albumin, BSA, were not protected from developing OVA-induced allergic airway disease. These findings demonstrated that maternal transfer of protection from development of allergic airway disease to offspring in this model of maternal Th1-type immunity was Ag specific.     

Peripheral tolerance induction using ethylenecarbodiimide-fixed APCs uses both direct and indirect mechanisms of antigen presentation for prevention of experimental autoimmune encephalomyelitis

MHC class II (MHC II)-restricted T cell responses are a common driving force of autoimmune disease. Accordingly, numerous therapeutic strategies target CD4(+) T cells with the hope of attenuating autoimmune responses and restoring self-tolerance. We have previously reported that i.v. treatment with Ag-pulsed, ethylenecarbodiimide (ECDI)-fixed splenocytes (Ag-SPs) is an efficient protocol to induce Ag-specific tolerance for prevention and treatment of experimental autoimmune encephalomyelitis (EAE). Ag-SPs coupled with peptide can directly present peptide:MHC II complexes to target CD4(+) T cells in the absence of costimulation to induce anergy. However, Ag-SPs coupled with whole protein also efficiently attenuates Ag-specific T cell responses suggesting the potential contribution of alternative indirect mechanisms/interactions between the Ag-SPs and target CD4(+) T cells. Thus, we investigated whether MHC II compatibility was essential to the underlying mechanisms by which Ag-SP induces tolerance during autoimmune disease. Using MHC-deficient, allogeneic, and/or syngeneic donor Ag-SPs, we show that MHC compatibility between the Ag-SP donor and the host is not required for tolerance induction. Interestingly, we found that ECDI treatment induces apoptosis of the donor cell population which promotes uptake and reprocessing of donor cell peptides by host APCs resulting in the apparent MHC II-independent induction of tolerance. However, syngeneic donor cells are more efficient at inducing tolerance, suggesting that Ag-SPs induce functional Ag-SP tolerance via both direct and indirect (cross-tolerance) mechanisms leading to prevention and effective treatment of autoimmune disease.     

A protease-activated pathway underlying Th cell type 2 activation and allergic lung disease

The respiratory allergens that induce experimental Th cell type 2-dependent allergic lung inflammation may be grouped into two functional classes. One class of allergens, in this study termed type I, requires priming with adjuvants remote from the lung to overcome airway tolerogenic mechanisms that ordinarily preclude allergic responses to inhaled Ags. In contrast, the other, or type II, allergen class requires neither remote priming nor additional adjuvants to overcome airway tolerance and elicit robust allergic lung disease. In this study, we show in an experimental model that diverse type II allergens share in common proteolytic activity that is both necessary and sufficient for overcoming airway tolerance and induction of pulmonary allergic disease. Inactivated protease and protease-free Ag fragments showed no allergenic potency, demonstrating that only active protease acting on endogenous substrates was essential. Furthermore, induction of airway tolerance could be aborted and allergic lung disease established by simply adding purified protease to a type I allergen. Thus, exogenous proteases are common to type II allergens and may be generally required to overcome the innate resistance of the airway to Th cell type 2 activation and allergic inflammation, raising concern for their potential contribution to diseases such as asthma.     

Tolerance induced by apoptotic antigen-coupled leukocytes is induced by PD-L1+ and IL-10-producing splenic macrophages and maintained by T regulatory cells

Ag-specific tolerance is a highly desired therapy for immune-mediated diseases. Intravenous infusion of protein/peptide Ags linked to syngeneic splenic leukocytes with ethylene carbodiimide (Ag-coupled splenocytes [Ag-SP]) has been demonstrated to be a highly efficient method for inducing peripheral, Ag-specific T cell tolerance for treatment of autoimmune disease. However, little is understood about the mechanisms underlying this therapy. In this study, we show that apoptotic Ag-SP accumulate in the splenic marginal zone, where their uptake by F4/80(+) macrophages induces production of IL-10, which upregulates the expression of the immunomodulatory costimulatory molecule PD-L1 that is essential for Ag-SP tolerance induction. Ag-SP infusion also induces T regulatory cells that are dispensable for tolerance induction but required for long-term tolerance maintenance. Collectively, these results indicate that Ag-SP tolerance recapitulates how tolerance is normally maintained in the hematopoietic compartment and highlight the interplay between the innate and adaptive immune systems in the induction of Ag-SP tolerance. To our knowledge, we show for the first time that tolerance results from the synergistic effects of two distinct mechanisms, PD-L1-dependent T cell-intrinsic unresponsiveness and the activation of T regulatory cells. These findings are particularly relevant as this tolerance protocol is currently being tested in a Phase I/IIa clinical trial in new-onset relapsing-remitting multiple sclerosis.     

Effects of systemic versus local administration of corticosteroids on mucosal tolerance

Respiratory exposure to allergen induces T cell tolerance and protection against the development of airway hyperactivity in animal models of asthma. Whereas systemic administration of dexamethasone during the delivery of respiratory Ag has been suggested to prevent the development of mucosal tolerance, the effects of local administration of corticosteroids, first-line treatment for patients with bronchial asthma, on mucosal tolerance remain unknown. To analyze the effects of systemic versus local administration of different types of corticosteroids on the development of mucosal tolerance, mice were exposed to respiratory allergen to induce mucosal tolerance with or without systemic or intranasal application of different doses of dexamethasone or prednisolone. After the induction of mucosal tolerance, proliferation of T cells was inhibited in tolerized mice, whereas systemic applications of corticosteroids restored T cell proliferation and secretion of Th2 cytokines. In contrast, inhaled corticosteroids showed no effect on both T cell proliferation and cytokine secretion. In addition, mice systemically treated with corticosteroids showed an increased airway hyperactivity with a significant lung inflammation, but also an increased T effector cells/regulatory T cells ratio in the second lymphoid organs when compared with mice that receive corticosteroids by inhalation. These results demonstrate that local administration of corticosteroids has no effect on the development of immune tolerance in contrast to systemically applied corticosteroids. Furthermore, although different concentrations of corticosteroids are administered to patients, our results demonstrated that the route of administration rather than the doses affects the effect of corticosteroids on respiratory tolerance induction. Considering the broad application of corticosteroids in patients with allergic disease and asthma, the route of administration of steroid substances seems crucial in terms of treatment and potential side effects. These findings may help elucidate the apparently contradicting results of corticosteroid treatment in allergic diseases.     

Long-lived Th2 memory in experimental allergic asthma

Although life-long immunity against pathogens is beneficial, immunological memory responses directed against allergens are potentially harmful. Because there is a paucity of information about Th2 memory cells in allergic disease, we established a model of allergic asthma in BALB/c mice to explore the generation and maintenance of Th2 memory. We induced disease without the use of adjuvants, thus avoiding Ag depots, and found that unlike allergic asthma in mice immunized with adjuvant, immunizing with soluble and aerosol OVA resulted in pathological lung lesions resembling human disease. To test memory responses we allowed mice with acute disease to recover and then re-exposed them to aerosol OVA a second time. Over 400 days later these mice developed OVA-dependent eosinophilic lung inflammation, airway hyperresponsiveness, mucus hypersecretion, and IgE. Over 1 year after recuperating from acute disease, mice had persistent lymphocytic lung infiltrates, Ag-specific production of IL-4 and IL-5 from spleen and lung cells in vitro, and elevated IgG1. Moreover, when recuperated mice were briefly aerosol challenged, we detected early expression of Th2 cytokine RNA in lungs. Taken together, these data demonstrate the presence of long-lived Th2 memory cells in spleen and lungs involved in the generation of allergic asthma upon Ag re-exposure.     

A critical role for C5L2 in the pathogenesis of experimental allergic asthma

The complement fragment C5a plays dual roles in the development of experimental allergic asthma. It protects from pulmonary allergy by a regulatory effect on dendritic cells during allergen sensitization, but is proallergic during the effector phase. C5a can bind to two distinct receptors (i.e., C5a receptor and C5a receptor-like 2 [C5L2]). The functional role of C5L2 in vivo remains enigmatic. In this study, we show in two models of OVA- and house dust mite (HDM)-induced experimental allergic asthma that C5L2-deficient mice are protected from the development of airway hyperresponsiveness, Th2 cytokine production, eosinophilic airway inflammation, serum IgE, or mucus production. Surprisingly, HDM-induced experimental asthma in C5L2-deficient mice was associated with increased pulmonary IL-17A production and increased airway neutrophil numbers. To directly assess the role of C5L2 on myeloid dendritic cells (mDCs) during allergen sensitization, we performed single or repeated adoptive transfers of C5L2-deficient mDCs into wild-type mice. HDM-pulsed C5L2-deficient mDCs induced strong Th2 cytokine production, which was associated with marked IFN-γ and IL-17A production, decreased eosinophil numbers, and reduced IgE production as compared with HDM-pulsed mDCs from wild-type mice. HDM stimulation of C5L2(-/-) mDCs in vitro resulted in production of Th17-promoting cytokine IL-23, which was absent in wild-type mDCs. Our findings suggest that C5L2 acts at the mDC/T cell interface to control the development of Th1 and Th17 cells in response to airway HDM exposure. Furthermore, it drives Th2 immune responses independent of mDCs, suggesting a complex role for C5L2 in the development of experimental allergic asthma.     

CARMA1 is necessary for optimal T cell responses in a murine model of allergic asthma

CARMA1 is a lymphocyte-specific scaffold protein necessary for T cell activation. Deletion of CARMA1 prevents the development of allergic airway inflammation in a mouse model of asthma due to a defect in naive T cell activation. However, it is unknown if CARMA1 is important for effector and memory T cell responses after the initial establishment of inflammation, findings that would be more relevant to asthma therapies targeted to CARMA1. In the current study, we sought to elucidate the role of CARMA1 in T cells that have been previously activated. Using mice in which floxed CARMA1 exons can be selectively deleted in T cells by OX40-driven Cre recombinase (OX40(+/Cre)CARMA1(F/F)), we report that CD4(+) T cells from these mice have impaired T cell reactivation responses and NF-κB signaling in vitro. Furthermore, in an in vivo recall model of allergic airway inflammation that is dependent on memory T cell function, OX40(+/Cre)CARMA1(F/F) mice have attenuated eosinophilic airway inflammation, T cell activation, and Th2 cytokine production. Using MHC class II tetramers, we demonstrate that the development and maintenance of Ag-specific memory T cells is not affected in OX40(+/Cre)CARMA1(F/F) mice. In addition, adoptive transfer of Th2-polarized OX40(+/Cre)CARMA1(F/F) Ag-specific CD4(+) T cells into wild-type mice induces markedly less airway inflammation in response to Ag challenge than transfer of wild-type Th2 cells. These data demonstrate a novel role for CARMA1 in effector and memory T cell responses and suggest that therapeutic strategies targeting CARMA1 could help treat chronic inflammatory disorders such as asthma.     

Nicotine primarily suppresses lung Th2 but not goblet cell and muscle cell responses to allergens

Allergic asthma, an inflammatory disease characterized by the infiltration and activation of various leukocytes, the production of Th2 cytokines and leukotrienes, and atopy, also affects the function of other cell types, causing goblet cell hyperplasia/hypertrophy, increased mucus production/secretion, and airway hyperreactivity. Eosinophilic inflammation is a characteristic feature of human asthma, and recent evidence suggests that eosinophils also play a critical role in T cell trafficking in animal models of asthma. Nicotine is an anti-inflammatory, but the association between smoking and asthma is highly contentious and some report that smoking cessation increases the risk of asthma in ex-smokers. To ascertain the effects of nicotine on allergy/asthma, Brown Norway rats were treated with nicotine and sensitized and challenged with allergens. The results unequivocally show that, even after multiple allergen sensitizations, nicotine dramatically suppresses inflammatory/allergic parameters in the lung including the following: eosinophilic/lymphocytic emigration; mRNA and/or protein expression of the Th2 cytokines/chemokines IL-4, IL-5, IL-13, IL-25, and eotaxin; leukotriene C(4); and total as well as allergen-specific IgE. Although nicotine did not significantly affect hexosaminidase release, IgG, or methacholine-induced airway resistance, it significantly decreased mucus content in bronchoalveolar lavage; interestingly, however, despite the strong suppression of IL-4/IL-13, nicotine significantly increased the intraepithelial-stored mucosubstances and Muc5ac mRNA expression. These results suggest that nicotine modulates allergy/asthma primarily by suppressing eosinophil trafficking and suppressing Th2 cytokine/chemokine responses without reducing goblet cell metaplasia or mucous production and may explain the lower risk of allergic diseases in smokers. To our knowledge this is the first direct evidence that nicotine modulates allergic responses.     

Antigen-nonspecific recruitment of Th2 cells to the lung as a mechanism for viral infection-induced allergic asthma

Respiratory viral infections have been shown to trigger exacerbations of asthma; however, the mechanism by which viral Th1-type inflammation exacerbates an allergic Th2-type disease remains unclear. We have previously shown that although adoptively transferred Th2 cells are inefficiently recruited to the lung in response to Ag, cotransfer of Th1 cells can increase accumulation of Th2 cells. In this study, we show that respiratory viral infection increases recruitment of resting Th2 cells specific for OVA even in the absence of OVA challenge. These findings suggest that the mechanism by which Th1-type inflammation enhances allergy is via an effect on recruitment. To study the role of the antigenic specificity of Th1 cells in the enhancement of Th2 cell recruitment and to determine whether virus-induced recruitment of OVA-specific Th2 cells may involve Th1 cells specific to a different Ag, we tested whether hen egg lysozyme-specific Th1 cells could synergize with OVA-specific Th2 cells. Challenge of mice that had received adoptively transferred Th1 cells plus Th2 cells induced the expression of inflammatory chemokines in the lung and increased both recruitment and activation of Th2 cells, leading to eosinophil recruitment, even in the absence of challenge with the Th2 Ag. Interestingly, as IL-5 supports eosinophilia, culture of resting Th2 cells with fresh APC induced production of IL-5 in the absence of specific Ag. Thus, Ag-specific activation of Th1 cells enhances the recruitment potential of the lung leading to recruitment and activation of Th2 cells. This implies that circulating Th2 cells in allergic individuals could enter the lungs in response to infection or inflammation and become activated to trigger allergy.     

Dendritic cells genetically engineered to express IL-10 induce long-lasting antigen-specific tolerance in experimental asthma

Dendritic cells (DCs) are professional APCs that have a unique capacity to initiate primary immune responses, including tolerogenic responses. We have genetically engineered bone marrow-derived DCs to express the immunosuppressive cytokine IL-10 and tested the ability of these cells to control experimental asthma. A single intratracheal injection of OVA-pulsed IL-10-transduced DCs (OVA-IL-10-DCs) to naive mice before OVA sensitization and challenge prevented all of the cardinal features of airway allergy, namely, eosinophilic airway inflammation, airway hyperreactivity, and production of mucus, Ag-specific Igs, and IL-4. OVA-IL-10-DCs also reversed established experimental asthma and had long-lasting and Ag-specific effects. We furthermore showed, by using IL-10-deficient mice, that host IL-10 is required for mediating the immunomodulatory effects of OVA-IL-10-DCs and demonstrated a significant increase in the percentage of OVA-specific CD4(+)CD25(+)Foxp3(+)IL-10(+) regulatory T cells in the mediastinal lymph nodes of OVA-IL-10-DC-injected mice. Finally, adoptive transfer of CD4(+) mediastinal lymph node T cells from mice injected with OVA-IL-10-DCs protected OVA-sensitized recipients from airway eosinophilia upon OVA provocation. Our study describes a promising strategy to induce long-lasting Ag-specific tolerance in airway allergy.     

Modulation of ovalbumin-induced airway inflammation and hyperreactivity by tolerogenic APC

Allergic asthma is mediated in part by unregulated Th2 inflammation in response to an allergen. Induction of peripheral tolerance by inoculation of Ags into the anterior chamber of the eye (ocular tolerance) before sensitization blocks Th2 responses. Thus, we proposed that induction of ocular tolerance to the allergen might modulate an ongoing allergen-induced Th2 pathogenesis in the lung. We initiated ocular tolerance in previously immunized mice in a classic mouse model of OVA-induced pulmonary allergic inflammation. In the model of ocular tolerance, the need for inoculation of Ag into the anterior chamber can be bypassed by i.v. inoculation of in vitro-generated tolerogenic (TGF-beta2-treated, Ag-pulsed) APC (tol-APC). We observed that with i.v. inoculation, such tolerogenic APC, but not control APC, reduced eosinophil and lymphocyte pulmonary infiltration in experimental mice. Similarly, production of Th2 cytokines (IL-4, -5, and -13), but not IFN-gamma, was reduced. Importantly, airway hyperresponsiveness and mucus production were significantly reduced after treatment with the tol-APC. We also show that in vitro suppression of IL-13 production from OVA-sensitized effector T cells was mediated by CD8+, not CD4+, T regulatory cells. Thus, i.v. inoculation of the tol-APC induced peripheral tolerance that suppressed Th2-mediated pathogenesis in the lungs of presensitized mice. The ability of the tol-APC to induce peripheral tolerance and suppress existing Th2 immune inflammation may lead to novel therapies for pulmonary allergic inflammation and its related pathology.     

Suppression of murine allergic airway disease by IL-2:anti-IL-2 monoclonal antibody-induced regulatory T cells

Regulatory T cells (Treg) play a decisive role in many diseases including asthma and allergen-induced lung inflammation. However, little progress has been made developing new therapeutic strategies for pulmonary disorders. In the current study we demonstrate that cytokine:antibody complexes of IL-2 and anti-IL-2 mAb reduce the severity of allergen-induced inflammation in the lung by expanding Tregs in vivo. Unlike rIL-2 or anti-IL-2 mAb treatment alone, IL-2:anti-IL-2 complexes dampened airway inflammation and eosinophilia while suppressing IL-5 and eotaxin-1 production. Mucus production, airway hyperresponsiveness to methacholine, and parenchymal tissue inflammation were also dramatically reduced following IL-2:anti-IL-2 treatment. The suppression in allergic airway disease was associated with a marked expansion of Tregs (IL-10(+)CD4(+)CD25(+) and Foxp3(+)CD4(+)CD25(+)) in the tissues, with a corresponding decrease in effector T cell responses. The ability of IL-2:anti-IL-2 complexes to suppress airway inflammation was dependent on Treg-derived IL-10, as IL-10(+/+), but not IL-10(-/-) Tregs, were capable of mediating the suppression. Furthermore, a therapeutic protocol using a model of established airway allergy highlighted the ability of IL-2:anti-IL-2 complexes to expand Tregs and prevent successive airway inflammation and airway hyperresponsiveness. This study suggests that endogenous Treg therapy may be a useful tool to combat the rising incidence of allergic airway disease.